1. Technical Field
The present invention relates to a method for exact positioning of a patient for radiotherapy or radiosurgery. The present invention relates furthermore to a method of three-dimensionally mapping an X-ray image.
2. Description of Related Art
Major advances have been made recently in dose planning in the fields of radiotherapy and radiosurgery. Attempts are being made to bring treatment ever nearer to radiosurgical dosing, i.e. to work with higher radiation doses in fewer sessions, preferably only in a single session concentrated to a target volume, for instance, a tumor. Although engineering the dosage is relatively successful, as mentioned, the fact that the patient or the body site to be irradiated can only be positioned relatively inaccurately is often an obstacle to high dosage applications administered in a single or a few fractions. This is why, in most cases, recourse is made to conventional fractionated radiotherapy involving repeat application in low dosage so as to avoid greater damage to healthy tissue.
To improve positioning, currently, a very inaccurate xe2x80x9cmanualxe2x80x9d method is used, in which an X-ray image of the patient""s body part is produced in a linear accelerator. This image is compared to a reference radiograph, previously obtained at the simulator (an X-ray unit, the geometry of which is identical to that of the linear accelerator). The X-ray image and the simulator image are then compared by the physician, for example, on a light box, the positioning error between the actual position of the patient and the desired position is measured with a ruler and the patient is moved accordingly. At the most, the physician may also have a center beam reticule and/or the contour of the outer boundaries of the site available in both images as a guideline. The boundaries of the site may be defined e.g. by blocks of lead or driven beam blinds. Even when comparing DDRs (virtual xe2x80x9csimulator imagesxe2x80x9d detected from a set of three-dimensional image data) instead of real simulator images, this method remains unchanged.
Disadvantageously, this kind of patient positioning is already inaccurate for the following reasons:
The images are projective and thus not true-to-scale (no uniform image scale exists). xe2x80x9cManualxe2x80x9d reading of the necessary correctional shift is inaccurate.
A three-dimensional correctional shift from two-dimensional images without computer assistance is possible only to a limited degree and requires a lot of experience.
Known from U.S. Pat. No. 5,901,199 is an iterative method of aiming radiation therapy beams at a treatment target using diagnostic computer tomography data, with the aid of which a plurality of digitally reconstructed radiographs (DRRs) is generated. These DRRs are continually generated and compared to an X-ray image produced in situ until one is found which is a suitable match. With the aid of the data obtained thereby, the position of the treatment unit or radiation beam is corrected so that the beam strikes the target of treatment.
The disadvantage in this method is the high computation requirement since, to start with, the DRRs have to be generated at random, and a lot of them need to be compared to the actual X-ray image. In particular, the method requires finding a xe2x80x9csmartxe2x80x9d algorithm to approximate the DRR matching each body segment and for each patient in a reasonable time period.
An object of the present invention is to propose a method for the exact positioning of a patient for radiotherapeutical or radiosurgical applications, which obviates the above-cited disadvantages of the prior art. It is in particular the intention to achieve a very precise repositioning of the patient in a simple manner and in a short time, and automatically where possible.
This object is achieved in accordance with the invention by a method for the exact positioning of a patient for radiotherapeutical/surgical applications comprising the steps:
a) pre-positioning the patient relative to a linear accelerator,
b) producing at least one X-ray image of the patient or one of his body parts in the vicinity of the radiation treatment target,
c) mapping the X-ray image,
d) generating at least one reconstructed radiograph from a three-dimensional set of patient scanning data corresponding to said X-ray image, especially isocentrically,
e) superimposing the reconstructed image and the X-ray image, and detecting the positional error electronically or computer-controlled on the basis of specific landmarks in both images, and
f) correcting the location of the patient on the basis of the detected positional error.
It is of advantage that repositioning as proposed in accordance with the invention is a relatively quick way of obtaining a very precise target radiation. The electronic or computer-assisted detection of the positional error enhances accuracy quite considerably as compared to the xe2x80x9cmanualxe2x80x9d method. Mapping the X-ray image permits including this input data with sufficient accuracy in the analysis, so that errors and delays in the repositioning are also avoided from this end.
Pre-positioning occurs preferably in a method in accordance with the invention by means of a computer-controlled and camera-controlled navigation and tracking system with the aid of artificial, in particular reflecting, marker arrangements on the patient and the treatment units. Such a navigation and tracking system is able to handle all tasks involved in position sensing during implementation of the method in accordance with the invention and outputting the corresponding information for example on a computer display.
However, pre-positioning the patient may also be carried out by means of skin markers on the patient, natural landmarks or laser markings.
In principle, it should suffice to produce simply one X-ray image and to generate a corresponding reconstructed image. However in preferred embodiments of the method in accordance with the invention, at least two or more X-ray images and a corresponding number of reconstructed images are generated from different directions, and each are analyzed by comparison to enable any tilting of the patient or of the patient carrier to be taken into account in computation.
The X-ray image may be advantageously produced using a linear accelerator. Such X-ray images are called EPID images(Electronic Portal Imaging Device images), and the corresponding images can be produced on a flat panel (e.g. amorphous silicon) on an X-ray film or on any other two-dimensional imaging medium.
On the other hand, it is, of course, possible to produce the X-ray images by a separate X-ray source, e.g. with the aid of two X-ray sources, secured overhead, which generate sequential (electronic) X-ray images on a detector (e.g. amorphous silicon). If the detector cannot be positioned in the isocenter for various reasons (e.g. rotation of the gantry), an offset needs to be taken into account, both in approximate positioning and in error correction.
Quite generally, the X-ray image may be produced on an image amplifier or detector, in particular on the amorphous silicon stated since, by using amorphous silicon (flat panel) distortions are minimized. However, of course, it is also possible to use a scanned X-ray film. The X-ray image may be produced either by an imaging system integrated in the linear accelerator or by a separate X-ray unit.
In an embodiment of the method in accordance with the invention, superimposing the X-ray image and the reconstructed radiograph is effectuated by marking and interleaving as controlled by the user on a computer display (e.g. using mouse, keyboard, touchscreen, joystick, etc). On the other hand, superimposing of the X-ray image and of the reconstructed image may also occur by computer-controlled automatic image fusion.
In preferred embodiments of the method in accordance with the invention, the reconstructed image or reconstructed images is/are generated as
digitally reconstructed radiographs (DRRs)
digitally composited radiographs (DCRs)
MIP images
or as any two-dimensional image reconstruction from a set of three-dimensional patient scan data.
The position of the patient is corrected in accordance with the invention advantageously by moving the patient table, in particular automatically operated and corrected by a computer-controlled and camera-controlled navigation and tracking system with markers on the patient and/or on the patient table. In principle, it is also possible to correct the position of the patient by operating the table manually.
In accordance with a preferred embodiment of the method in accordance with the invention, in the steps c) and d) cited above, a plurality of reconstructed images is generated, which are then superimposed and compared to the mapped X-ray image, electronically or computer-controlled, until a reconstructed image is found which corresponds to the X-ray image, with the aid of which the positional error is then detected.
In this case, there is no need for isocentric reconstructed images since it is possible to increasingly approximate the desired reconstructed image by computer approximation procedures (algorithms). This embodiment is particularly of advantage since it permits a wider scope in patient pre-positioning. By using a mapped X-ray image, finding the corresponding reconstructed image is quicker and more precise.
The invention relates furthermore to a method of three-dimensionally mapping an X-ray image comprising the steps:
producing an X-ray image of the patient,
detecting the three-dimensional position of the X-ray unit while producing the X-ray image.
inserting markers in a predetermined or specific position relative to the X-ray source in the beam path thereof whilst producing the X-ray image, and
computing, from the geometry of the X-ray unit and from the position of the markers in the X-ray image, the precise three-dimensional imaging situation of the X-ray image.
By means of the above method in accordance with the invention, it is now possible to precisely determine the three-dimensional position of an X-ray image. This is particularly important when this X-ray image is used as an input parameter for further mapping and positioning, since this already enables this input value to be defined precisely mapped and correctly. During image formation at a linear accelerator, the position of the image amplifier or of the film on its holder is often not 100% fixed relative to the radiation source and relative to the isocentric beam. An error of this kind can be excluded by mapping each individual X-ray image.
In this arrangement, it is now possible to determine the three-dimensional position of the X-ray source and/or of the image receiver, as well as of a patient carrier, by means of a computer-controlled and camera-controlled navigation and tracking system with markers. Furthermore, detecting the three-dimensional position of the X-ray source and/or image receiver may also be done via scaled detection means on these units.
In an embodiment of the mapping method, the X-ray image is produced by a linear accelerator for radiotherapy/radiosurgery with an image receiver, a carrier for the markers being fixedly positioned in front of the radiation source. These markers appear on the X-ray image to then make it possible to precisely compute the three-dimensional imaging situation of the X-ray image from their known distance away from the radiation source as well as from their known marker geometry.
Advantageously, a linear accelerator with a leaf collimator is used in front of the radiation source, the markers being formed by collimator leafs driven into the radiation path to a specific degree. In this arrangement, the zone of the leaf collimator may either already have the radiation shape or it may be specially shaped for mapping, the leafs being extended asymmetrical only edgewise so as not to detriment the image. Generally, the distances between the radiation source and the marker carrier or leaf collimator are fixed and known. If need be, however, a calibration with a phantom may provide even more precise values.
In accordance with the invention, it is of course possible, and preferably also provided, to use the method described for three-dimensionally mapping an X-ray image, utilizing an X-ray image within the scope of the method described for the exact positioning of a patient.